The desirability of viewing representations of signals and their signal characteristics either alone or in the context of other signals or events has increased significantly over the years. The importance of visual representation has been increased by the multiple analytical methods which have been implemented with fewer and fewer hardware components. More recently, it has been possible to include these signal analyzers within the body of the oscilloscope to provide complex signal analysis within a relatively limited physical dimension. The signal characteristics which can be displayed arise from generalized sampled data measuring instruments included within the oscilloscope. Time domain instruments such as digital storage oscilloscopes, also provide computing capabilities such as rise-time, fall-time and pulse-width as well as additional signal processing capabilities including filtering, spectrum analysis such as Fast Fourier Transform (FFT) and long term signal storage for later recall and comparison. Signal processing computers provide additional signal measurement and parameter display capabilities. However, a digital computing oscilloscope incorporating all the above features cannot merely aggregate the individual instrument functions. Generalized expansion of the oscilloscope facility results in an instrument as unwieldly as an entirely analog oscilloscope of the same capability having every parameter adjustment assigned to a particular control among many controls. Each new function, with its particular analog signal processing and control characteristics makes different requirements on the oscilloscope facilities. The functions must be integrated in a coherent manner to cooperate with each other.
One approach is to reduce the flexibility of each function to limit the number of controls by which the operator may adjust the instrument. However, the sacrifice of flexibility is typically the opposite of what the instrument was created to provide.
An alternate approach is to generalize the system wherein its function is determined according to a general computer program. One such system may comprise a microcomputer and a rack of IEEE 488 bus-compatible instruments. The user must be a programmer familiar with the use of each of the instruments and the specific communication protocol. A further disadvantage that often results in such systems is that important parameters become embedded in the program and are accessible only by tedious reassembly process. Checkout becomes difficult when the immediate results cannot be easily scrutinized. In such systems, the functions retain their flexibility but it is the user group which is limited, primarily to a group sophisticated in the particular system assembled.
In digital controlled equipment, when the proper parameter values have been established and the data taken for a particular reading, it is often necessary to reestablish and review the event occurrence. This is complicated through the need to readjust the oscilloscope to various settings at several different sequential periods during the test operation. Moreover, comparisons to prior test results, such as comparison of one signal to a prior signal, has heretofor been limited to large scale computer systems, and not for laboratory test instruments where they would be most useful.
Furthermore the signal to be measured by a digital oscilloscope must be sampled with high accuracy and resolution in both sample amplitude and sample time period. Ultimately, the digital oscilloscopes' processing capability are limited by the input signal frequency and resolution accuracy.